Conventionally, in communications performed via a backbone network, a communication apparatus in the network relays data, messages, and others (for example, refer to Japanese Patent Application Laid-open No. 2004-343199).
The communication apparatus uses a predetermined communication protocol. In particular, a communication apparatus using Open Shortest Path First (OSPF) broadcasts, within the network, link information indicative of a link between apparatuses and link state between apparatuses.
This communication apparatus receives the link information to generate topology information indicative of how all communication apparatuses are connected with each other in the network.
Each communication apparatus refers to the topology information to search for a route to an arbitrary destination, for example.
Meanwhile, as the network grows bigger, the link information to be broadcasted further increases, resulting in overgrown topology information retained in each communication apparatus.
To address this problem, a technique has been developed in which the network is divided into a plurality of areas and the broadcast destination of the link information from each communication apparatus is restricted within an area.
Specifically, a node selected from an area or, for example, a totally different server, summarizes link information within the area. Then, the communication apparatus, which summarizes the information representatively, broadcasts resulting summarized information to another area.
Examples of summarizing techniques include a node abstraction technique of abstracting areas into a single node (refer to “OSPFv2 Routing Protocols Extensions for ASON Routing”, Dimitri Papadimitriou, URL that includes “tools.ietf.org/html/draft-ietf-ccamp-gmpls-ason-routing-ospf-03”.) and a link abstraction technique of abstracting links among apparatuses within an area into links only between area border nodes each serving as an entrance to its own area and area border nodes each serving as an exit to another area.
In the techniques mentioned above, each representative communication apparatus receives and retains summarized information generated in another area.
By referring to the summarized information, it is possible to know how the areas are connected to each other to construct the network, whereby it is possible to search for an approximate route to relay to an arbitrary destination, with the knowledge of which areas to pass through.
However, the summarized information does not include detailed information about links between the apparatuses within each area. Therefore, whether the routes found as a result of the search are redundant cannot be known.
Therefore, redundant routes to an arbitrary destination cannot be set based on the summarized information.
Moreover, it is impossible to find redundant routes to an arbitrary destination and to find a maximum reservable bandwidth of the set redundant routes based on the summarized information.